It is well known that very often problems occur when a user attempts to program his VCR to record a television show at a given time and date. To eliminate these problems VPS (Video Program System) and VPT (VCR Programmed by Teletext) were introduced. These systems are in common use in Europe. VPT was formerly known as VPV (Videotext Programmed VCR).
The original purpose of adding a supplementary VPS signal to the image-representative TV broadcast signal was to simplify the use of home videocassette recorders (VCR's). Prior to the introduction of VPS, these VCR's were programmed by means of a timer, which started and stopped the VCR according to the time when the desired television program of interest was scheduled for transmission.
Occasionally, the program of interest could not be correctly recorded, for example, due to a delay in the completion of the previous television program. The VPS signal was intended to overcome this drawback by providing an accurate indication of the starting time of a new program. A more detailed description is available in the literature, (see for example, "VPS-Ein neues System Zur beitragsgesteuerten Programmaufzeichnung", Rundfunktech-nische Mitteilungen, Heft 4,1985).
The VPS program identification code occupies four bytes (11-14) on data line 16 in the vertical blanking (retrace) interval of a TV broadcast signal. The four bytes of the VPS signal contain information such as day and time of day of the originally scheduled start of a particular TV program to be broadcast. A more detailed description of the VPS signal is provided below.
To make the programming of VCR's even more convenient, the VPT system was developed (see "Videotext programmierte Videoheimgerate (VPV)" Rundfunktechnische Mitteilungen, Heft 3, 1986).
VPT involves the automatic transfer of the necessary information to a VCR from the program pages of the teletext service. The user causes the display of a directory of teletext program pages, and moves a cursor to the desires television program title. Upon pressing an appropriate button on a remote control, the necessary VPS program identification information is transferred to the VCR.
It should be mentioned that the scheduled time and the VPS-time are not always identical. This is because the scheduled time is updated whenever a particular program runs overtime and subsequent programs are delayed or a schedule is otherwise changed. The VPS time always remains unchanged since it is assigned to the program and not to the actual final broadcast time.
By use of VPS and VPT, incorrect recording of a desired television program, caused either by time-shifted television programs or by errors made by manual keying in of the data such as start time stop time, date, and program source (channel), is thus greatly eliminated.
Unfortunately, even if the VPS and VPT systems are used, the recording of the desired television program can still fail because of VPT or VPS errors originating from the studio side. Television programs are announced on VPT program schedule pages two weeks in advance. If such a page contains incorrect VPS data and a VCR is programmed with the incorrect data, the recording of that particular television program will, of course, fail. Usually, such errors are noticed and corrected by the editors of these pages sometime after the incorrect data is entered. Even though such errors are later corrected on the VPT pages by the editor, a conventional VCR cannot adapt its preprogrammed data to such corrections. Another source of errors which may prevent the recording of desired television programs is the entry of incorrect VPS codes onto data line 16, also caused by mistakes made at the broadcaster side.